1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method thereof. Specifically, it relates to an image forming apparatus capable of effectively preventing generation of black spots derived from leaked current from a cleaning device, and an image forming method using the same.
2. Description of the Related Art
Conventionally, in an electrophotographic system image forming method such as a copying machine and a printer, electrophotographic photoconductors (photoconductor drums) are widely used as a latent image carrier body. Such a common image forming method using the electrophotographic photoconductors is carried out as follows.
That is, by charging the surface of the electrophotographic photoconductor to a predetermined potential by a charging means and directing a light beam thereto from a LED light source with an exposing means, the potential at the exposed portion is attenuated by the light beam so as to form an electrostatic latent image corresponding to the original image. Then, by developing the electrostatic latent image with a developing means, a toner image is formed on the electrophotographic photoconductor surface. Finally, by contacting or setting close to the electrophotographic photoconductor and a transfer means, the toner image is transferred onto an intermediate transfer body or a paper.
On the other hand, according to the image forming method, a problem is involved in that toner not contributing to the image formation called the residual toner easily remains on the surface of the electrophotographic photoconductor after the transfer. Moreover, in the case an amorphous silicon photoconductor is used as the electrophotographic photoconductor, a problem arises in that foreign substances such as the discharge products easily adhere onto the electrophotographic photoconductor surface derived form the charging means.
Then, in order to solve such problems, a method for removing the foreign substances such as the residual toner and the discharge products on the electrophotographic photoconductor surface by adding a minute amount of a polishing agent to the toner to be used and using a polishing roller and a cleaning blade in combination has been proposed (see for example the patent documents 1 and 2).
More specifically, the patent document 1 discloses an image forming method using a toner including a polishing agent and an amorphous silicon drum as a photoconductor of developing the toner with a developing means, and polishing and cleaning the amorphous silicon drum surface with a sliding roller after the transfer, wherein an elastic layer for scavenging the polishing agent is provided on the sliding roller surface for scavenging the polishing agent in the toner by the elastic layer so as to polish and clean the drum surface with the scavenged polishing agent.
On the other hand, the patent document 2 discloses an image forming apparatus comprising a photoconductor, a sliding roller for sliding on the photoconductor surface via a toner, a scraping member for scraping off the toner on the photoconductor surface, and a toner conveying means for carrying the toner scraped off by the scraping means parallel to the roller axial direction, wherein the toner feeding rate at the intermediate portion of the sliding roller axial direction is set lower than the feeding rate at the both end portions in the sliding roller axial direction.
However, according to the image forming methods disclosed in the patent documents 1 and 2, since the characteristics of the toners are not adequately understood, the toner stored in the cleaning device can easily be charged excessively due to the friction by means of the cleaning blade and the polishing roller. That is, the phenomenon of the sudden discharge of the charge accumulated in the toner in the vicinity of the cleaning blade so as to provide the leak current flowing toward the electrophotographic photoconductor surface has been observed.
Therefore, there are problems that such leak current causes damages to the surface of the electrophotographic photoconductor, and the black spot generates on the formed image.
In particular, in the case that a method of transferring the toner supported on the surface of the latent image carrier body to the transfer body from the lower position is adopted, a phenomenon that tends to form the air gap between the toner in the vicinity of the cleaning blade and the surface of the electrophotographic photoconductor has been observed. Therefore, not only the polishing property with respect to the surface of the electrophotographic photoconductor is poor, but also the leak current generation is facilitated by means of the charge accumulated in the toner in the vicinity of the cleaning blade so as to further increase the black spot generation, and such problems still remain.    [Patent document 1] JPH10-63157A (Claims, FIG. 1)    [Patent document 2] JP2005-49620A (Claims, FIG. 1)